Corrosion inhibiting composition containing a neutral amide and c3-c8 volatile amine



3,458,453 Patented July 29, 1969 US. Cl. 252-392 4 Claims ABSTRACT OF THE DISCLOSURE Neutral amides of C -C hydrocarbon monocarboxylic acids and alkylene polyamines combined with volatile amines, such as C -C alkylamines and pyridines, in Weight ratios of the amine to the amide from about 1:1 to about 1:8, when introduced into petroleum hydrdocarbon stocks undergoing fractionation in a petroleum refinery, display an unexpected synergism as a corrosion inhibitor, drastically reducing the corrosion of metal in fractionation equipment.

The present invention relates to new corrosion inhibiting compositions for use in petroluem refinery operations, particularly applicable to such phases of petroleum refining as steam distillation and fractionation of various crude oil feedstocks.

It is, of course, well known that the metal equipment in petroleum refineries, and particularly the equipment constructed of steel and copper-containing Admiralty Metal,undergoes extensive corrosion, with yearly rates of as high as 100 mils and even higher having been recorded to occur in the upper portions of steam distillation and fractionation columns and in their related equipment, such as heat exchangers and condensers serving to collect and recover (or recycle) hydrocarbon fractions which distill overhead.

In the past, in order to provide against this undesirable corrosion, corrosion inhibitors have been injected countercurrently to the flow of vapors rising overhead in a still or tower. Among such inhibitors, a number of materials containing amino-nitrogen atoms in thier molecular structure have been found effective, since the presence of amino-nitrogen is known to be often co-extensive with some degree of anticorrosion activity. However, one is never able to foretell with certainty that an amino-nitrogen containing inhibitor will be adequately and consistently effective in preventing corrosion, particularly in preventing corrosion of the distillation and fractionation equipment. A particularly disturbing observation by those concerned with the reduction of corrosion is that such corrosion inhibitors do not function at a steady rate, but that, in fact, their elfectiveness varies in the case of individual inhibitors. Some of these corrosion-inhibiting additives, although introduced in the refinery distillation equipment in very low concentrations, have been found to be carried over into the product and to affect adversely the quality of gasoline or jet fuel, and to cause engine deposits, while others, even though good anti-corrosion agents, are apt to precipitate from gasoline because of an insufficient solubility in hydrocarbons. Still other additives have a tendency to cause emulsification, for some Water (moisture) is nearly always present in commercial gasoline and jet fuel.

As a consequence, the search for and the deveolpment of new and improved corrosion inhibitors for use in petroleum refinery operations with the aim of prolonging the life of refinery metal equipment and assuring production of more satisfactory products, in particular gasoline, continues unabated.

INHHBITING CDMPOSITION CON-' While searching for such new and improved corrosion inhibitors, I noted that neutral amides of C 43 aliphatci, cycloalpihatic and aliphatic-cyclic hydrocarbon monocarboxylic acids and alkylene polyamines particularly lend themeslves for use as corrosion-inhibiting additives to hydrocarbon feedstocks undergoing distillation and fractionation at petroleum refineries. The term alkylene polyamines, as employed in this description, is intended to refer to polyamines represented by the general formula in which m is a whole number from 2 to 3 and nis a whole number from 1 to 3. Neutral amides of aliphaticcyclic (alicyclic) hydrocarbon monocarboxylic acids known in the petroleum art under the generic term of naphthenic acids, because they contain at least one naphthene ring with a paraflinic side-chain (or chains) branching off the ring are preferred, since their use in the hydrocarbon feedstocks will suppress foaming at the same time.

The molecular weight of these acids lies in the broad range from about 150 to about 400, While their acid nurnbers may be from about 360 to about 140. A complete description of these acids is found in the specification of US. Patent No. 2,430,953, issued to Rouault. Particularly satisfactory for the preparation of neutral amides mentioned hereinabove are naphthenic acids whose average molecular weights range from about 250 to about 310, with acid numbers being from about 220 to about 180.

As examples of individual, particularly effective neutral amides of aliphatic, cycloaliphatic and alicyclic monocarboxylic acids for inhibiting corrosion in accordance with the present invention, there may be mentioned neutral amides of diethylene triamine and naphthenic acids (trinaphthenoyl amides of diethylene triamine) and neutral amides of diethylene triamine and oleic acid (trioleyl amides of diethylene triamine) The group of alkylene polyamines suitable for the production of neutral amides of the present invention as described by the general formula hereinabove includes diethylene triamine, dipropylene triamine, tetraethylene pentamine and tripropylene tetramine.

The neutral amides are introduced into the hydrocarbon feedstocks at the refinery in the form of concentrates, that is, dissolved in suitable organic solvents, for instance, in a compatible hydrocarbon solvent and/ or an aliphatic alcohol, or yet a mixture of such hydrocarbon and alcohol solvents, the solvent portion of the concentrate preferably boiling between about 150 and 400 F. The concentrate may be formulated to contain from about 10 to about by weight of the solvent. Actually, little difiiculty is experienced in introducing the amide inhibitors at a convenient point of an overhead system in a steam distillation column or other like fractionation equipment in the refinery. The solution of the amide is fed thorugh an inlet tubing or an atomizer at the top of the column at a rate which depends on the refiux ratios and the size of the equipment involved, as well as on the corrosiveness on the hydrocarbon stock being processed, the pH of the system and the tendency of the particular metal in the refinery equipment to corrode. For instance, assuming a conventional refinery reflux ratio of about 4:1 and a throughput of about 800 barrels per hour, 0.1 gallon per hour of a neutral amide inhibitor of the present invention would provide about 4 p.p.rn. (parts per million) of the inhibitor in the overhead flow, although higher concentrations may be used if desired.

Prior to being tested in the actual operation in the refinerys distillation equipment, individual neutral amides were tested in a specially designed laboratory apparatus resembling a crude oil still. This apparatus permits of estimating the performance of refinery corrosion inhibitors in the laboratory, but under conditions of corrosive atmosphere essentially approximating the conditions which prevail in industrial equipment, that is, in actual operation of refinery stills. The apparatus is calibrated with reference to known corrosion inhibitors. It consists of a 2-liter flask connected to a column 15" high and 3" wide, equipped with 4 porous trays. A side arm (V2" in diameter) serves to convey vapors from the column to a condenser. This arm protrudes well above the top tray into an area covered by a detachable dome which is arranged to permit suspending from it metal strips or probes to be exposed to the rising overhead vapors. A tube is provided in the dome for introducing (pumping in) the corrosion inhibitor solution into the system, so, however, that the inhibitor being introduced :at a relatively low level has the minimum opportunity to wet the probe directly.

The corrosion conditions are provided by boiling in the flask a 30% solution of MgCl in water mixed with a 50/50 (by volume) blend of toluene and n-heptane. The phase in the overhead under the dome is, accordingly, a mixture of vapors of hydrocarbon and water at a temperature of about 90 to 95 C. A small amount of hydrogen chloride is liberated from MgCl as the mixture is being distilled. This accelerates corrosive attack on polished and cleaned mild steel metal probes, 5 cm. high and 1 cm. wide, so that results may be obtained within 6 hours. The results are rated visually on a scale ranging from 1 to 6: the rating of 1 referring to a spotless probe; the rating of 6 to an entirely corroded probe.

After having been screened in this laboratory equipment, the neutral amide corrosion inhibitors were submitted to testing in the refinery by feeding them into the crude hydrocarbon at the top of a distillation column. It was observed, however, that the neutral amides, although etfective in inhibiting corrosion of those portions of the equipment (in the column) where the liquid phase could physically contact the metal surface, were not capable to supress or reduce sufficiently the corrosion in those portions where only vapor was present, specifically in the upper portionat the top or dome of the distillation column. It was then surmised that the nonvolatile neutnal amides, particularly the neutral amides of naphthenic acids, failed to provide an adequate protective film on the metal surfaces inside the very top of the column, a substantial portion of the incoming amide being entrained by hydrocarbon vapors to the heat exchanger or condenser, while the balance gravitated downward into the column.

It was then that I found that by combining said, otherwise effective, anti-corrosive neutral amide of a C -C aliphatic hydrocarbon monocarboxylic acid with a volatile amine, e.g., cyclohexylamine, in 'a critical weight ratio 4 of the amine to the amide of about 1:1 to 1:8 and preferably 1:2 to 1:4, a synergistic combination could be achieved which, present in the hydrocarbon feedstocks in amounts from 1 to 5 ppm. and higher, but, usually, no higher than 30 ppm, permits to reduce drastically the metal corrosion not only in those portions of the equipment where the liquid phase conditions prevail, but also at the top of the column in the vapor phase. This discovery of coaction of the amine and the amide was entirely unexpected because, as it will be shown hereinafter, not only were the neutral amides alone insufficient to reduce the corrosion in the top of a distillation column, but the volatile amines also, if used alone, were likewise dismally ineffective in combating the metal corrosion in the distillation system. The amide-amine composition is introduced into the hydrocarbon feedstocks in the form of concentrated solutions of from about 20 to about by weight in a hydrocarbon or an alcohol, as mentioned hereinbefore with reference to neutral amide inhibitors.

In the so-discovered anticorrosion additive combination, the volatile amine component is an amine from the group of C -C alkyland cyclo-alkylamines, pyridine and alkyl-substituted pyridines, the common characteristic of these volatile amines being that the number of carbon atoms in their molecular structure does not exceed eight. Alkyl-substituted pyridines commercially available under the designation of high boiling pyridines are preferred.

The following Table I contains the results of a number of laboratory tests carried out in the apparatus described hereinabove: without any corrosion inhibitor be ing added; adding single neutral amide inhibitors (e.g., naphthenoyl amides or oleylamides); also, using volatile amines alone; furthermore, using certain inhibitors of the prior art; and, finally, using combinations of neutral amide inhibitors with volatile amines. The naphthenoyl amides were derived from petroleum naphthenic acids of an average molecular weight of 250 with acid number of 224.

The neutral amides of naphthenic acid and diethylene triamine to be used in these tests were prepared as follows: 30.8 pounds of naphthenic acid were charged into a 10- gallon kettle together with 6.35 pounds of diethylene triamine and 1 gallon of benzene. The mixture was heated up to about 350 C. to take out 1500 ml. of water. The product obtained was a naphthenoyl amido-imidazoline of diethylene triamine. Next the temperature of the mixture in the kettle was dropped to C., and 15.4 pounds of naphthenic acid were added, whereupon the whole mixture was stirred for 5 hours at 100 C., yielding a neutral trinaphthenoyl amide of diethylene triamine.

A trioleyl amide of diethylene triamine was produced in a similar fashion.

In the table which follows, the word diethylene triamine are appreviated to DETA.

TABLE I.LABORATORY TESTING OF METAL CORROSION Parts per Million Corrosion Inhibitor (25% by wt. concentrate Parts of Hours Test No in kerosene) Feed on Test Rating Observations (Mild Steel 5" x 1" Probes 1 None 6 4 Pitting and dark scale.

Commercial inhibitor. trademark Kontol 200 6 3 Uniformly coated with protective film of oxide.- Neutral DETA-trinaphthenoyl amide 200 6 3 Surface dull. do 200 6 1.5 Probe soaked 5 minutes in inhibitor solution prior to test. Neutral DETA-trioleyl amide. 200 6 1. 5 Do. 6. do 200 6 3.5 No soaking treatment. Suriace dark and pitted. 7 Commercial n-butylamine. 200 6 2 Filmdon tprpibes is not sufiieiently strong; spotty an pi e 8 Commercial di-n-butylamine 200 6 3.5 N o protection.

Commercial tri-n-butylamine 200 6 4 Do. 10. Commercial inhibitor, trademark Unicor M 200 6 3 Film is not sufficiently strong. 11 Neutral DElA-trinaphthenoyl amide (5 parts)+ 200 6 1 Spotless probe surface.

cyelohexylamine (1 part). 12 Neutral DETAtrinaphthenoyl amide (2 parts)+ 200 ii 1 Do.

cyclohexylamine (1 part). 13.... Neutral DETA-trioleyl amide (4 parts) +n-butyl- 200 6 1 Do.

amine (1 part). 14 Neutral DETAtrinaphthcnoyl amide (2 parts) 100 6 1 Do.

n-butylaminc (1 part). 15 Neutral DE'lA-trinaphthenoyl amide (2 parts) 200 U 1 Do,

high boiling pyridines (1 part).

The data in the table clearly bring out the unexpected superiority of the combination of (1) neutral amides of aliphatic and aliphatic-cyclic (naphthenic) acids and (2) volatile amines, as contrasted with the effectiveness of individual neutral amides and volatile amines, and as contrasted with the several commercially available corrosion inhibitors.

This unexpected superiority of the synergistic combinations of such neutral :amides with volatile amines was then tested and unambiguously reafiirmed in a series of tests in actual refinery operations, the observations having been carried out for a period of at least 30 days. This test series involved a battery of several distillation units (crude stills), in which straight-run gasoline was recovered overhead at a 4:1 reflux ratio.

The corrosion-inhibiting composition was introduced through an inlet tubing at the top of each column at rates which provided different concentrations of the inhibitor combination inside the units of the battery. The pH of the water in the overhead was maintained at about 6.0-7.0 by injecting the necessary volumes of ammonia, which only acted as a pH regulator but not as a corrosion inhibitor. Corrosion rates were measured with the aid of steel and Admiralty alloy probes and then compared with the corrosion rates in mils per year, recorded in the operation of recovering straight-run gasoline without introducing any corrosion inhibitors. In this latter instance, the column after 30 days was observed to undergo corrosion at rates corresponding to an average of 250 mils per year in the top of the column, 200 mils in the vapor line, :and 200 mils in the run-down line.

The following tabulation (Table II) of several determinations of this series, comparing the data obtained with individual representative neutral amides and volatile amines alone with the results achieved in accordance with the invention using synergistic amide-amine combinations, unambiguously illustrates the improvement in corrosion rates due to the use of these latter.

drocarbon monocarboxylic acid from the group consisting of C C hydrocarbon monocarboxylic acids and naphthenic acids with an alkylene polyamine of the general formula wherein m is a whole number from 2 to 3 and n is a whole number from 1 to 3, and (2) a volatile amine from the group consisting of C -C alkyl amines and C -C cycloalkylarnines, pyridine and alkyl-substituted pyridines, the number of carbon atoms in the molecule of said amine not exceeding 8, and the weight ratio of the amine component to the amide component being from about 1:1 to about 1:8.

2. A composition for inhibiting corrosion as defined in claim 1, wherein the neutral amide component is an amide of naphthenic acid having a molecular weight in the range from about 180 to about 400.

3. A composition for inhibiting corrosion as defined in claim 1, wherein the weight ratio of the volatile amine component to the neutral amide component is from about 1:2 to about 1:4.

4. An additive concentrate capable of being incorporated into hydrocarbon stocks undergoing fractionation in petroleum refinery equipment, said concentrate consisting essentially of a solution of from about 20 to about 90% by weight of a corrosion-inhibiting composition of a neutral amide and a volatile amine, defined in claim 1, in an organic solvent boiling in the range of from about 150 to about 400 F. and selected from the group consisting of hydrocarbon solvents, aliphatic alcohols and mixtures of these hydrocarbon and alcohol solvents.

TABLE II.-CORROSION RATES COMPARED IN REFINERY OPERATION Parts per Milli Inhibitor Composition as a 25% Solution Test No. in Kerosene 1 20% by weight of neutral amide of naphthenic acid (aver. mol. wt. 230; mol. wt. range 200-280) and diethylene triamine, plus 5% by weight of high boiling Py idine. 2 do 3 do 4 20% by weight of neutral amide of naphthenic acid (aver. mol. wt. 230; mol. wt. range 200-280) and diethylene triemine, plus 5% by weigbt of 5 cyglohexylamine.

n 6 A neutral trioleyl amide (octadecenoyl) amide of diethylene triamine. No inhibitor. Run on straight-run gasoline 8 A neutral amide of naphthenic acid (aver. mol. 3. 1

wt. 230; mol. wt. range 200-280) and diethylene triamine. Oyclohexylamine High boiling pyridines 0 ky wIight of neutral trioleyamide of diethyleilng triamine plus 5% by weight cyclohexylam e.

coo:

Corrosion Rate in Mils per Year on Parts of At top 0! In Vapor Feed Stock Column In Run- Lme Down Line References Cited UNITED STATES PATENTS 3,107,221 10/1963 Harrison et a1. 252390 X 3,294,705 12/1966 Kautsky 252390 OTHER REFERENCES Condensed Chemical Dictionary, Reinhold, 1961, p. 326.

RICHARD D. LOVERING, Primary Examiner I. GLUCK, Assistant Examiner U.S. Cl. X.R.

fineries, which consists of (1) a neutral amide of a hy- 203--7; 208-47; 252--8.55, 390, 394 

